Fix from SF patch #633359 by Greg Chapman for SF bug #610299:

The problem is in sre_compile.py: the call to
    _compile_charset near the end of _compile_info forgets to
    pass in the flags, so that the info charset is not compiled
    with re.U. (The info charset is used when searching to find
    the first character at which a match could start; it is not
    generated for patterns beginning with a repeat like '\w{1}'.)

Lib/sre_compile.py

@@ -399,7 +399,7 @@ def _compile_info(code, pattern, flags):
                 table[i+1] = table[table[i+1]-1]+1
         code.extend(table[1:]) # don't store first entry
     elif charset:
-        _compile_charset(charset, 0, code)
+        _compile_charset(charset, flags, code)
     code[skip] = len(code) - skip
 
 STRING_TYPES = [type("")]

Lib/test/re_tests.py

@@ -666,4 +666,5 @@ else:
     # bug 410271: \b broken under locales
     (r'\b.\b', 'a', SUCCEED, 'found', 'a'),
     (r'(?u)\b.\b', u, SUCCEED, 'found', u),
+    (r'(?u)\w', u, SUCCEED, 'found', u),
     ])